Fluorescent lighting systems with leading reactive components for maintaining full load voltage equal to the noload voltage



3,335,321 REACTIVE D NOW WITH LEADING LOA LTAGE 2 Sheets-Sheet 1 B A 4 m6 6 NW F 97 W m F V y "SHELLEY KRASNOW KRAS SYSTEMS OR MAINTAINING FULLVOLTAGE EQUAL TO THE NO-LOAD VO Original Filed Oct. 8 1956 Aug. 8, 1967s FLUORESCENT LIGHTING COMPONENTS F BUSES Aug. 8, 1967 s, ow 3,335,321

FLUORESCENT LIGHTING SYSTEMS WITH LEADING REACTIVE COMPONENTS FORMAINTAINING FULL LOAD VOLTAGE-EQUAL TO THE NO-LOAD VOLTAGE OriginalFiled Oct. 8, 1956 2 Sheets-Sheet 2 I 27 27 E1916 WW, 7

INVENTOR United States Patent 3,335,321 FLUORESCENT LIGHTING SYSTEMSWITH LEAD- ING REACTIVE COMPONENTS FOR MAINTAIN- IN G FULL LOAD VOLTAGEEQUAL TO THE NO- LOAD VOLTAGE Shelly Krasnow, Fairfax, Va. (315 TudorLane, Manassas, Va. 22110) Continuation of application Ser. No. 246,880,Dec.

21, 1962, which is a division of application Ser.

No. 614,599, Oct. 8, 1956. This application Feb.

18, 1966, Ser. No. 533,763

11 Claims. (Cl. 315-244) This is a continuation of applicantsapplication Ser. No. 246,880, now abandoned, filed Dec. 21, 1962, whichin turn is a division of his application Ser. No. 614,599, filed Oct. 8,1956.

This invention relates to dynamo-electric machines and the circuits tobe used therewith. There will be described herein a particular type ofstructure and a circuit to be used in conjunction with such structurefor high frequency fluorescent lighting.

Use of frequencies above 60 cycles with the conventional type offluorescent lamp has been found to yield markedly superior results inoperation and in life of the lamps. Frequencies of 360 and 400 cycleshave been used for this purpose. However, as is recognized in this art,frequencies above 400 cycles yield even superior results. Although theprinciples of construction of the machine to be described herein and ofthe circuit for use therewith, will not be altered by the frequency, theparticular example chosen for illustration herein will be designed tooperate at 840 cycles.

As will be obvious to those skilled in this art, many of the features ofconstruction of the dynamo-electric ma,- chine will be appropriateandapplicable to other similar structures such as motors, magnetos,electrically or magnetically operated clutches, servo-systems, etc.

It is one purpose of the invention to provide a compact unitaryeflicient structure for the conversion of low frequencies such as 25, 50or 60 cycles to higher frequencies.

It is a further purpose of the invention to provide a highly efficientmagnetic structure for the rotor of a dynamo-electric machine and toprovide such structure and associated stator to deliver a wave form witha high percentage of harmonic components, suitable for use by highfrequency fluorescent lighting systems.

It is a further purpose of the invention to provide a mechanicallystrong rotor structure designed to withstand high rotational speeds. p

It is a further purpose of the invention to provide a stator structurefor use in conjunction with the improved rotor described in order toprovide a convenient meansv of obtaining the desired frequency,harmonics and voltage.

It is a further purpose of the invention to provide an armature windingin which the voltage stress between adjacent conductors used thereinwill be reduced to aminimum and will thus avoid danger of breakdown.

It is a further purpose of the invention to provide an external circuitespecially matched to the properties of the converter to be described soas to obtain superior results for the converter and circuit combination.

It is a further purpose of the invention to provide a circuit associatedwith the converter to be described, which will maintain a relativelyconstant voltage for all conditions of load, without the use of anyregulating equipment.

It is a further purpose of the invention to permit the use of aconverter of the general type described in conjunction with a load ofhigh leading power factor, without the necessity for complex regulatingdevices.

These and other purposes of the invention will be apparent from thespecifications taken in conjunction with the drawings in which:

FIGURE 1 shows a cross-sectional view of a complete motor-generatorfrequency converter according to the invention.

FIGURE 2 shows an end view of the converter shown in FIGURE 1 viewedfrom the generator end.

FIGURE 3 shows a cross-sectional view of the rotor and stator of thegenerator shown in FIGURE 2, taken across the plane 22.

FIGURE 4 shows a partial cross-section of a portion of the rotor shownin FIGURE 3 taken across the plane 33.

FIGURE 5 shows a schematic view of the armature windings utilized in thegenerator shown in FIGURE 2.

FIGURE 6 shows the connection diagram for the interconnection of thearmature coils shown in FIGURE 5.

FIGURE 7 shows a wiring diagram of the armature as presented to theexternal circuit.

FIGURE 8 shows a typical external circuit including a fluorescent lampand its auxiliaries, suitable for connection to the generator shown inFIGURE 2.

FIGURE 9 shows the method of magnetization of the magnets shown in theportion of the rotor structure pictured in FIGURE 4.

FIGURE 10 shows the magnetic lines of force due to the magnets in FIGURE4.

FIGURE 11 shows an oscillogram of the wave form obtained with thegenerator shown in FIGURE 2.

Referring now particularly to FIGURE 1, 1 shows a completemotor-generator assemblage. This consists of a two-part housing, element2 being the motor portion and 3 the generatorportion. Within portion 2is a motor stator 4 and free to rotate therein, a motor rotor 5. Themotor may be of any of the types familiar in the art. Thus it may be adirect current type, single phase alternating current, 2 or 3-phasealternating current, etc. A preferred type for most applications will bethe conventional squirrel-cage type of 3-phase induction motor.

Within housing 3 is a generator stator 6 and free to rotate therein,generator rotor 7. A shaft extends through and is rigidly attached torotors 5 and 7 respectively and rests in bearings 9 and 10 respectively.Connection is made to the motor for energisation thereof through leads11. The output of the generator portion is delivered throughleads 11.The energisation of motor 2 will cause rotation of shaft 8 andconsequent rotation of rotor 7 within stator 6. This will generateelectric power to be delivered through leads 11. I

The detail of the generator portion is further shown in FIGURE 2.Although many of the features of the invention may be attained withgenerators of electromagnetically excited types, the particular type tobe described herein will be one utilizing permanent magnets forexcitation. The rotor 7 of this machine is constructed about awheel-like member with an outer periphery of a ferromagnetic material. Apreferred form consists of a hub portion 13 which fits upon shaft 8,attached by means of a web or spokes 16 to rim 17. The material of rim17 may be mild or wrought steel, wrought iron, cast steel or a grade ofmalleable iron of the general type known as Magtiz. The portions 13 and16 need not be of the same material, although it has been foundconvenient to construct the wheel portion 7 of a single casting orforging of the shape shown. Mounted upon machined surfaces 18 on rim 17are a plurality of magnets 19. In the type of construction shown, eachmagnet defines a pole. The machine may therefore have a minimum numberof 2 magnets or may have any desired larger number, depending upon thefrequency desired and the rotational speed to be used. In the particularexample shown, 28 magnets are utilized with a rotational speed of 3600r.p.m., yielding 840 cycles.

The magnets 19 are of a form different than those heretofore used, beingof frusto-pyramidal form with the broadest portion mounted facing thecenter of the rotor 7. The reasons for the selection of the formdescribed will be treated further herein.

Resting upon magnets 19 are pole pieces of ferromagnetic material 20.These are generally of highly permeable material such as silicon steeland may be made of a solid piece of steel or of a series of siliconsteel laminations resting edgewise upon the magnets and fastenedtogether so as to constitute an integral pole piece. The pole pieces 20are preferably made with sharply defined corners 23 and also with slots24 cut into the surface of the pole face. The purpose of the sharpcorner 23 and the slot 24 is to introduce harmonics into the generatedwave.

After preliminary assembly of elements 16, 19 and 20, molten aluminumalloy is cast around the peripheral part of the structure and allowed tosolidify. After solidification, the rotor may be finally machined todimension and provided with balancing holes 14, between each pair ofmagnets 19, 19.

The magnets 19 may be made of cast Alnico magnet material, cobalt steel,or any of the other commonly available permanent magnet materials.

In the specific example shown a strongly magnetic permanent magnetmaterial is utilized. However, with a leading power factor load, such asmet with in a fluorescent lamp and capacitor ballast arrangement, aweakly magnetic permanent magnet material or even ordinary steel oriron, may be used for magnets 19.

Balancing of the rotor 7 to correct the inevitable misdistribution ofweight therein and to prevent vibration, is effected by placing heavyslugs such as lead within the balancing holes 14.

The conventional methods of balancing by drilling out material are notsuitable for use with this structure, since the aluminum being a lightmaterial, will require removal of an undue amount in order to effectbalance. Removal of such amounts will seriously Weaken the rotorstructure since its strength is greatly dependent upon the strength ofthe cast aluminum.

The use of the tapered magnets 19 in the manner shown permits thecasting or drilling of larger balancing holes 14, without weakening orendangering the strength of the cast aluminum portion 12. Balancingslugs may be placed toward either edge of the rotor 7 in order to effectdynamic as well as static balance.

The taper of the magnets as shown has been found to yield superiorresults in many respects. It has been common in the art to provideindividual magnets for the purpose described of parallel form such asrectangular blocks or with a taper facing inwardly and having the largerbase portion at the periphery, rather than toward the mounting structureof the rotor. In contradistinction, in the present invention, thebroader portion of the magnet rests against the flange. One consequenceof the use of the tapered magnet has already been mentioned, namelymaking possible the enlargement of balancing hole 14. Another advantageresides in the physical strengthening of the rotor. After the casting ofthe molten aluminum, during solidification thereof the aluminum willshrink. This will cause it to exert a compressive stress inward upon theelements cast therein. Since the magnets have tapered sides, the resultof this stress will be to press the magnets more tightly against the rim17 and thus hold the magnet in tight magnetic contact with said rim 17.The centrifugal stress on the magnet due to rotation of the rotor willbe resisted by the aluminum cast therearound. In effect, the aluminumwill have a tapered pocket in which each magnet rests and thecentrifugal force will have the effect of pressing the magnet in upagainst the tapered pocket, the latter being a particularly effectiveform for resisting such stress.

A still further advantage of the tapered form of the magnet will be seento follow from the magnetizing process that is utilized for magnetizingmagnets 19 after assembly in the rotor 7. The magnetizing fixtureconsists of a removable horse-shoe shaped member 21, the faces of whichare machined to be in close contact with the pole faces 2020. The coil22 serves to energize horseshoe member 21 and to cause establishment ofa magnetic flux therein. A high value of the direct current is passedthrough coil 22 and a high value of magnetic flux is thereby set up inthe magnetic circuit composed of member 21, pole faces 20, magnets 19and rim 17.

It will be seen that in the magnetizing process, useful lines of forcesuch as (a) will pass through the entire structure, while non-useful orparasitic leakage lines of force (b) will pass through the air betweenmagnets 19, 19. These will not serve to magnetize the magnet and in anyevent will not magnetize it in the direction desired. The closer theflanks of the magnets 19, 19, the greater will be the leakage and thegreater robbing of the useful flux utilized for magnetization. Thetapered form of the magnet reduces the leakage flux by increasing thedistance between the sides of the magnets. Magnetization is thereforeimproved.

Superior performance during operation also results from the use of thetapered magnets. Thus, as shown in FIGURE 10, the flux produced by themagnet passes through pole pieces 20 and into the armature 15. However,prasitic lines of leakage flux also exist between the magnets and serveto reduce the total amount of the useful working flux. By tapering themagnet distance between the faces is increased and the leakage factorreduced.

A still further advantage of the tapered form, where very hard magneticmaterials of the type of Alnico must be utilized, and such materials arecast, is that the tapered form makes it much easier to mold and draw thecastings from the mold.

In operation of high frequency fluorescent lighting systems, it has beenfound that the performance improves the higher the frequency, up tofrequencies of the order of 20,000 cycles. However, as one proceedsabove 400 cycles, the obtaining of substantial amounts of powereconomically becomes more and more difficult. A practicable frequency,in the particular example described herein is 840 cycles. However, it isdesirable to have the advantages of still higher freqencies, and this isobtained to a considerable extent by superposing high frequencyharmonics upon the fundamental 840 cycle wave. These high frequencyharmonics have been obtained in the present instance by the shaping andslotting of the pole faces as shown in FIGURE 4, by eliminating the skewin the stator structure customarily used, and by utilizing a winding asshown in FIGURE 5. The use of these expedients singly or in combination,will yield a wave form with a high percentage of harmonics as shown inFIGURE 11, FIGURE 11(a) representing the oscillogram of the wave form atlight load and FIGURE 11(b), the wave form at substantial load.

It has also been found that the conducting or amortisseur bars placedcustomarily in the pole faces 20, may be omitted with a consequentincrease in the generated harmonic content.

FIGURE 5 shows the winding pattern used for the stator 6 of thegenerator. The stator may, for example, have 84 slots. The windingpattern for each of the independent phases is shown. It will be seenthat each coil spans three slots and that the coil sides for adjacentcoils lie in the same slot. The phases are displaced by one tooth. Thewindings for each of the three phases are identical. A tap is broughtout from the fourteenth coil of each phase. This is for the neutral orground connection 26 mentioned herein. Except for the common groundneutral connection, the phases are electrically in dependent.

Use of the winding described has been found to yield a large percentageof odd harmonics, particularly the third harmonic. This is advantageous,as further detailed herein.

The connection diagram for the generator is shown in FIGURE 6.

FIGURE 7 shows the wiring diagram of the generator as presented to theexternal load. It will be seen that three individual windings areprovided, each displaced in phase relationship from the other. Although3 phases are shown, any number of phases, either one or a plurality may.be utilized, without departing from the spirit of the invention. A3-phase arrangement is shown, because 3-phase generators are most usual.Each of the coils has terminals 25, 25 and a center tap 26 which isgrounded, thus connecting the center points of all coils to a commonterminal and to ground. The advantage of this is that no point in eitherthe generator or external circuit is more than half the total voltageabove ground potential. The voltage between terminals 28-28 may be, forexample, 400 volts or 600 volts. The voltage across terminals 2727 and2525 may have the same value as the voltage across terminal 2828.Alternatively, where it is desired to use fluorescent lamps of differentlengths, each with difl erent voltage requirements, the voltage betweenterminals 28-28 may for example, be 600 volts and that between 27--27,for instance, 400 volts. Due to the structure of the generatorsdescribed herein, the application of load to one pair of terminals, forexample 2828, will have relatively little effect on that produced byload on terminals of another phase, 2 727. The elimination of aregulator as further described herein, makes it possible to wind themachine to produce different voltages from each phase withoutinterference with each other.

As a still further alternate, a tap 29 may be placed in any of thewindings. The voltage then obtained may be either that between either ofterminals 28 and 29 or between the ground terminal such as 26 and theterminal 29. This feature is especially valuable where there are to beutilized only a few lamps employing a different voltage than that of themajority of lamps utilized in the system.

Alternatively, a tap such as 29, may be utilized for monitoring orcontrol purposes or for the operation of auxiliary devices other thanlamps.

A typical circuit employing fluorescent lamps is shown in FIGURE 8. Hereterminals 25, 25 are the leads from one phase of the generator. A switch33 controls the flow of current in this circuit, and for the sake ofgenerality a choke 32, a condenser 31 and a resistance equivalent to thedissipative load of the lamp 30, are represented in series.

, FIGURE 8 may be taken to represent not merely one lamp but a series oflamps and their equivalent circuit. a For the sake of economy, acapacitor ballast 31 is utilized to limit the current flowing in thelamp 30. The value of capacitor 31 will depend upon the frequencygenerated by the generator, the harmonics present therein, the voltageof the generator and the current that is desired to flow through thelamp 30.

In order to effect economy in the wiring, switches and the converterunit itself, it is desirable to correct or partially correct the leadingpower factor due to the lamp 30 and the capacitor 31. The net powerfactor of this combination is usually of the value of 30% leading. Thechoke coil 32 may be place in series with each individual capacitor, butis preferably used in series with or parallel across the circuitscomprised of a number of lamps and their respective capacitor ballasts31.

It has been found with the generator described, that the regulation;i.e., the change in voltage upon application of load can be brought to alow figure, very equipment.

The preferred method of adjusting power factor in a circuit of the typeshown in FIGURE 8, is to adjust the value of choke 32 until a netloading power factor is obtained, corresponding to that figure for whichthe generator will have a minimum regulation or a regulation within thedesired voltage tolerance.

For example, plus or minus 5% may be tolerated in the output voltage. Itis then necessary only to correct the power factor to such a value thatthe net change in voltage will be no greater than plus or minus 5%.

This procedure makes it possible to utilize a smaller choke than wouldotherwise be necessary, with consequent economy in first cost and inoperation. It also makes it possible to avoid entirely the correction ofcircuits containing only a few lamps, since the overall effect of theirload and power factor on the entire system, will be so small as to beneglected. The use of a wave with a high percentage of harmonics makesthe choke more effective than it would be for the fundamental frequencyalone and therefore permits a still further reduction in the size of thechoke.

Still further features of construction which make it possible to reducethe size of the choke, and in some cases to eliminate it altogether, aregiven below:

If the motor 2 in FIGURE 1 is chosen so as to show a great speed dropwith application of load, in other words, to have a high slip, if aninduction motor, the application of load will cause a reduction in speedof the generator 3, which will have the effect of reducing the terminalvoltage and also reducing the frequency. Both of these effects will tendto reduce the voltage applied across the circuit shown in FIGURE 8 andwill tend to reduce the voltage and current through lamp 30. However,the load imposed by the lamp 30 with its capacitor 31 is leading incharacter and a leading load of the magnitude and power factor notedabove, has the effect of raising the terminal voltage of the generator.Thus, the terminal voltage increasing effect and the terminal voltagedecreasing effect due to slowing down of the motor and generator, willtend to oppose each other and to tend toward a constant voltagecondition. This, as noted above will make it possible to reduce the sizeof the choke and in some cases to eliminate it altogether.

A still further correcting circumstance occurs in the case of the waveform. The effect of the capacitive load of the type described, will beto suppress the harmonics and to leave a wave with the greaterproportion of the fundamental. Since the capacitor 31 will tend to passthe high frequency components more readily than the lower frequency, theremoval of these high frequency components or the reduction of theirpercentage will cause a reduction in the net current flowing through thelamp 30.

At the same time, the application of the leading load to the generatorwill tend to cause an increase in the terminal voltage of. thegenerator. This tendency to increase voltage and thus increase thecurrent through the lamp 30 will at the same tfme be counterbalanced, atleast in part, by the reduction in the harmonics as noted above.

Any of the expedients noted above tending toward the maintenance of theconstant voltage condition may be used singly or in any combination.They will in all cases, tend toward achieving the ideal of a constantcurrent through lamp 30, regardless of the total load in the system.

Where a direct current motor is utilized for the driving means in FIGURE1, a governor may be utilized on the shaft of the motor, or other speedsensitive devices may be utilized, in order to maintain relativelyconstant speed. Alternatively, the speed control device may be selectedso as to have a droop suitable for correction of the voltage increasewhich tends to be caused by the application of the leading load on thegenerator.

The rotating system composed of rotor 7 of the generator and rotor ofthe motor on shaft 8, will have a high moment of inertia, particularlysince the rotor 7 is in the shape of a fly wheel. This will tend to givethe converter a stabilizing effect and to resist the effects of shortperiod disturbances on the input supply lines. The latter are oftencaused by switching on or off of large motors.

Since with the usual type of induction motor, the input voltage hasrelatively little effect on the operating speed, the converter as shownwill be quite insensitive to voltage changes on the input supply line.The output voltage will, in general; tend to remain more constant thanthe input voltage, so that a high quality of lamp operation may beobtained from a low quality of supply.

The use of the correction systems noted above will avoid the use ofcomplex and delicate regulating auxiliaries. Since the converterdescribed is intended for use in localities where skilled personnel arenot ordinarily available for maintenance of delicate and complexequipment, the elimination of such equipment and the necessity thereforis an important step in the more widespread use of the high frequencysystems.

Where alternating current is utilized for the drive of the motor 2, nobrushes will be required in the motor and since the generator portionlikewise does not utilize brushes, the installation may be madeexplosion-resistant or explosion-proof.

A plurality of converter units as shown in FIGURE 1 may have theiroutputs connected in parallel. For such purpose, the internal impedancesof the generator portion of the machines are made nearly identical andthe terminal voltage for a given condition of load are made nearlyidentical. The machines may then be interconnected in parallel so as toshare the load when the latter becomes too great for'one machine tohandle alone.

As an alternate, the motors 2 may be synchronous motors, particularlybrushless types of synchronous motors. If the stators 6 of thegenerators are all arranged so as to bear the same angular relation tothe stator 4 of their respective motors, the outputs of the generatorsmay then be connected in parallel, since they will always be in the samephase relationship and will remain so due to the constant speedcharacteristics of the synchronous motors.

As will be obvious to those skilled in the art, the features ofconstruction of the converter units may be applied singly or in anycombination or may be applied to purposes other than the operation ofhigh frequency fluorescent lighting systems.

The principles of matching of load and converter or load and generatormay be applied to loads other than those due to fluorescent lamp andtheir auxiliaries.

The scope of the invention is indicated by the appended claims.

What is claimed is:

1. In a high frequency lighting system, an unregulated constantexcitation dynamo-electric alternating current generator as the sourceof power therefor, said generator having zero regulation for loads of aparticular leading power factor, a gas discharge lighting load and aballast having a capacitive reactance to limit the current in said loadto the desired value, an inductive reactance, connected to said ballastand load and of such reactance value to yield, in combination with saidload and said ballast a net leading power factor, substantially equal tosaid particular power factor, whereby, upon application of said lightingload, the terminal voltage of the said generator will not departsubstantially from its no-load value.

2. A system as in claim 1, in which the generator is a permanent magnettype and the lighting load is composed of one or more fluorescent lamps.

3. A system as in claim 1, in which the lighting load is composed of aplurality of fluorescent lamps, each with its own capacitive ballast.

4. In a system having a rotary dynamo-electric alternating currentgenerator and a plurality of loads energized thereby, an unregulatedgenerator with constant excitation having zero regulation for loads of aparticular leading power factor, a plurality of loads, each withcapacitive and inductive members, said members being adjusted one to theother to secure substantially said particular leading power factor foreach said load, whereby when any single load or any combination of saidplurality of loads is connected in power receiving relation to saidgenerator, the terminal voltage thereof will be substantially unchanged.

5. In a system as set forth in claim 4, said generator being a permanentmagnet type.

6. In a method of maintaining substantially constant terminal voltage inan unregulated, dynamo-electric alternating current constant excitationgenera-tor, notwithstanding variable magnitude of total load due tovariation in number of a plurality of loads, the steps of determiningthat leading power factor value for which said generator voltage in theloaded condition will not depart substantially from its no-load terminalvoltage, of adjusting the capacitive and inductive values in eachindividual load to a net leading power factor substantially equal tosaid determined power factor and of applying any desired combination ofsaid loads in energy receiving relation to said generator, whereby saidgenerator terminal voltage will remain substantially unchanged,notwithstanding application of load.

7. In a system for maintaining constancy of terminal voltage for anunregulated dynamo-electric alternating current generator, saidgenerator having zero regulation for loads of a particular power factor,reactive means to limit current within the load circuit, additionalreactive means having a reactance opposite to the first reactive meansand of value to yield a net power factor due to the load and bothreactive means substantially equal to said particular power factor andmeans to interconnect both reactive means and the load to saidgenerator, whereby the generator voltage will be substantially unchangedupon application of said load.

8. In a high frequency lighting system, an unregulated constantexcitation dynamo-electric attending current generator as the source ofpower therefor, said generator having negative regulation for loads of aleading power factor less than a particular value and positive or zeroregulation for loads of all other power factors, a gas dischargelighting load and a ballast having a capacitive reactance to limit thecurrent in said load to the desired value, an inductive reactance,connected to said ballast and load and of such reactance value to yield,in combination with said load and said ballast a net leading powerfactor less than said particular value, whereby upon application of saidlighting load, the terminal voltage of said generator will rise aboveits no-load value.

9. In a system as set forth in claim 8, said generator being a permanentmagnet type.

10. In a method of maintaining substantially constant terminal voltagein an unregulated dynamo-electric generator, the steps of determiningthat power factor value for which said generator will maintain itsterminal voltage at load to substantially that value at its terminals atno load, of determining the power factor of a selected load to beenergized by said generator, of determining further that reactivemodification in magnitude and direction required to bring said loadpower factor to said generator power factor value, of applying saidreactive modification to said load, and of connecting the so modifiedload to said generator in energy receiving relation therewith, wherebyupon said connection the terminal voltage of said generator will remainessentially at its no-load value.

11. In a system for minimizing voltage change on application of load toa generator in which an unregulated constant excitation dynamo-electricgenerator having zero regulation for a particular power factor energizesa load having a power factor differing substantially from saidparticular power factor, a correcting reactive member connected to saidload and having a reactive value proportioned to the power factor ofsaid load to provide a combined load power factor equal substantially tosaid particular power factor, whereby when said combined load isconnected to said generator in energy receiving relation therewith, aminimal change in terminal voltage of said generator relative to no loadvoltage will result.

References Cited UNITED STATES PATENTS OTHER REFERENCES ElectricalEngineering, by Clarence V. Christie, McGraw-Hill Book Co., New York,N.Y., 1917, pages 10 315, 316 and 3&7.

JAMES W. LAWRENCE, Primary Examiner. C. R. CAMPBELL, Assistant Examiner.

8. IN A HIGH FREQUENCY LIGHTING SYSTEM, AN UNREGULATED CONSTANTEXCITATION DYNAMO-ELECTRIC ATTENDING CURRENT GENERATOR AS THE SOURCE OFPOWER THEREFOR, SAID GENERATOR HAVING NEGATIVE REGULATION FOR LOADS OF ALEADING POWER FACTOR LESS THAN A PARTICULAR VALVE AND POSITIVE OR ZEROREGULATION FOR LOADS OF ALL OTHER POWER FACTORS, A GAS DISCHARGELIGHTING LOAD AND A BALLAST HAVING A CAPACTIVE REACTANCE TO LIMIT THECURRENT IN SAID LOAD TO THE DESIRED